The Tabuu Saga is the first "saga" in the Lapisverse, with the story arc being part of the first three Fighters of Lapis games (plus MicroLapis and Lapis Hearts). The story spans five whole games with the main villain being Tabuu.
Fighters of Lapis
Tabuu begins an invasion in the Lapisverse and the Fighters of Lapis must stop him from creating his own world out of their worlds. At the end, Tabuu fuses with Darkseid and attempts to destroy the Fighters of Lapis but fails and is defeated. After the credits Tabuu apparently fuses with Missingno.
Fighters of Lapis 2
Things begin to glitch up as Missingno apparently attacks the Lapisverse. With the help of Ashura, they can battle Missingno and discover that Tabuu was pulling the strings all along. The Fighters of Lapis and their new friend Ashura battle Herobrine and Tabuu and defeat Tabuu for what it seems to be forever.
A world where toys coexist and rule has been discovered by Darkseid. He attempts to destroy it after the events of Fighters of Lapis 2, as he finds out that Zim, who betrayed him in the events of Fighters of Lapis, is gathering things from there for his lastest plan to destroy the Earth. Darkseid is turned into a toy by Zim's toy gun, but Zim is turned into one as well after accidently shooting himself. Darkseid then rounds up some of his own toys, and attempts to take over this world!
It is discovered though, that Darkseid is actually being controlled by the daughter of Degen, Degen Jr. who raises Degen from Hell as well as an army of undead. After defeating the Degens, the god of the Lapisverse returns Zim and Darkseid back to their normal states and decides that the worlds need to be separated for their own good.
Darkness shrouds the worlds as Sheyna tries to rescue them with her keyblade. Honestly, I never finished this, so let's just say that she finds Tabuu or something to be part of it and then destroys him, leaving him to fuse with Sauron or something.
Fighters of Lapis 3
Mario and the other Fighters of Lapis find out Tabuu is back. While they attempt to defeat him, he utterly destroys them and takes over the Lapisverse, and now they have to fight back. During the Final Battle, he destroys the Lapisverse with a black hole and the Fighters of Lapis accept their fates as the black hole destroys the Lapisverse. Meanwhile, the trophy of Mac ends up in a new universe and imagines everything before.